Basin and Range Province Quiz
Normal faulting, horst-graben topography (10 questions).
Basin and Range Province Quiz: Quick Study Notes
The Basin and Range Province, a vast physiographic region covering much of the Western United States and parts of Mexico, is a classic example of extensional tectonics. Its distinctive landscape is characterized by a repetitive series of alternating mountain ranges (horsts) and down-dropped valleys (grabens), sculpted primarily by normal faulting over millions of years. This unique topography provides a living laboratory for understanding how the Earth’s crust responds to stretching and thinning.
Key Concepts
Formed by tensional forces pulling the crust apart. The hanging wall moves down relative to the footwall. Key mechanism for Basin and Range formation.
Elevated, block-faulted mountain ranges. These blocks are left standing relatively high as adjacent blocks subside along normal faults.
Down-dropped valley floors or basins. These blocks subside between parallel normal faults, often filling with sediments and forming playas or temporary lakes.
The geological process where the Earth’s crust is stretched and thinned, leading to the formation of normal faults, horsts, and grabens. Driven by lithospheric forces.
Key Takeaways
- The Basin and Range Province is defined by its characteristic horst-and-graben topography.
- Normal faulting is the primary geological process responsible for creating this landscape.
- Horsts are uplifted blocks forming mountain ranges, while grabens are subsided blocks forming valleys.
- This topography results from significant east-west extensional forces acting on the North American lithosphere.
- Graben basins are often filled with thick sequences of alluvial and lacustrine sediments.
- The region exhibits clear evidence of crustal stretching and thinning.
Frequently Asked Questions
What is the Basin and Range Province?
It’s a vast physiographic region in western North America characterized by alternating, parallel mountain ranges (horsts) and valleys (grabens), formed by crustal extension.
How do normal faults create horst and graben topography?
Normal faults form when the Earth’s crust is stretched. As the crust pulls apart, blocks of land slide down along these faults, forming grabens (valleys), while the land between these down-dropped blocks remains elevated, forming horsts (mountains).
What is the difference between a horst and a graben?
A horst is an uplifted block of crust situated between two normal faults that dip away from it, forming a mountain range. A graben is a down-dropped block of crust between two normal faults that dip towards it, forming a valley or basin.
What causes the extensional forces in the Basin and Range?
The extension is generally attributed to a combination of factors, including the subduction of the Farallon Plate beneath North America, the subsequent rollback of the subducting slab, and possibly the gravitational collapse of the previously thickened crust.
Where is the Basin and Range Province primarily located?
It spans across much of Nevada, Utah, Arizona, and parts of California, Oregon, Idaho, New Mexico, and extending into Mexico.
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